1. Field of the Invention
This invention relates to a method of generating cutting passes for a complex curved surface and, more particularly, to a method of generating cutting passes for a complex curved surface using data indicating the vertical relationship of a plurality of curved surfaces constituting a complex curved surface.
2. Description of the Related Art
A curved surface of a three-dimensional metal mold or the like on a design drawing is generally expressed by a plurality of section curves, but no profile data is shown for the shape of the area lying between a section curve and the next adjacent section curve.
In numerically controlled machining, it is essential that machining be carried out so as to smoothly connect these two section curves despite the fact that the profile between them is not given. In other words, this means that machining must be performed by generating the curved surface between the two section curves from such data as that indicative of the section curves, recording on an NC tape the data concerning the generated curved surface, and carrying out machining in accordance with commands from the NC tape. To this end, there has been developed and put into practical use a method comprising generating a plurality of intermediate sections in accordance with predetermined rules from several sections of a three-dimensional curved body from data specifying section curves, finding a section curve (intermediate section curve) on the curved body based on the intermediate sections, and generating a curved surface of the three-dimensional body based on the plurality of generated intermediate section curves. For example, the details are described in U.S. Pat. No. 4,491,906, registered in the U.S. on Jan. 1, 1985, and U.S. Pat. No. 4,589,062, registered in the U.S. on May 5, 1986. This method is useful in generating a smooth curved surface from section data.
Depending upon the type of machining, there are cases where it is necessary to generate a complex curved surface obtained by combining a plurality of three-dimensional curved surfaces. Methods of generating these complex curved surfaces have also been proposed. For example, refer to the specification entitled "Method of Generating Complex Curved Surface" of U.S. Pat. No. 4,855,921, registered in the U.S. on May 18, 1987. In this proposed method of generating cutting passes on a complex curved surface, cutting passes are generated on a complex curved surface by the following steps (a) through (e), described with reference to FIGS. 4 and 5:
(a) Data are entered in advance for specifying three-dimensional curved surfaces, namely a first curved surface SS1, a second curved surface SS2, a third curved surface SS3 and a fourth curved surface SS4 constituting a complex curved surface SS, and the following data are entered for specifying the vertical relationship of these combined surfaces:
______________________________________ CUT SS1 (1) COMP SS2, A (2) COMP SS3, A (3) COMP SS4, A (4) ______________________________________
In the foregoing, (1) signifies obtaining a cutting pass from the curved surface SS1, (2) signifies obtaining a cutting pass upon transferring to the curved surface SS2 when the Z value becomes larger than that of the curved surface SS1, and (3), (4) similarly signify obtaining cutting passes upon transferring to the curved surfaces SS3, SS4. Further, the alphabetic character "A" is a qualifier which signifies making a transfer when the Z value becomes larger than that of the curved surface defined immediately ahead.
(b) This is followed by entering data specifying one line of intersection CL1 on a predetermined plane (e.g., the X-Y plane), as well as a rule for specifying a number of lines of intersection CLk (k=1, 2, . . . ) on the X-Y plane based on the line of intersection CL1.
(c) Thereafter, section curves 11k, 12k, 13k, 14k (see FIG. 5) are obtained. These are section curves which result when the respective curved surfaces SS1, SS2, SS3, SS4 are cut by a section PLk whose line of intersection with the X-Y plane is a k-th line of intersection CLk among the aforementioned number of lines of intersection.
(d) Of projection points Pk.sub.1, Pk.sub.2 obtained by projecting a point Pk (k=1, 2 . . . ) on the intersection line CLk onto each of the section curves, one projection point Pk.sub.2, decided by the above mentioned vertical relationship data, is taken as a point on a cutting pass Pak (FIG. 4) for cutting the complex curved surface.
(e) Cutting passes of the complex curved surface SS are generated by collecting the cutting passes Pak (k=1, 2, . . . n) corresponding to the intersection lines CLk (k=1, 2, . . . n).
There are cases where it is desirable to generate the complex curved surface SS from a cutting pass direction different from that of the cutting pass Pak, e.g., from the direction of a cutting pass Paj in FIG. 4. In such a case, irrespective of the fact that it will suffice merely to know the vertical relationship between two curved surfaces (SS1 and SS3) when obtaining the cutting pass Paj, the vertical relationship between curved surfaces (SS2 and SS4) that have no relation to the cutting pass Paj must also be considered and found based on all of the curved surface vertical-relationship data
______________________________________ CUT SS1 COMP SS2, A COMP SS3, A COMP SS4, A ______________________________________
Consequently, the processing for generating the cutting passes Paj requires a great deal of time.